Tarinder recently had a look at three budget CPUs, two from AMD and one from Intel, to see if any of them was worth considering if your budget is tight. Here's a snippet.
Which value processor should you choose?. If your budget resembles a shoestring then a bottom-end Sempron (Socket A, obviously) or Celeron D 320 are the natural choices. Both CPUs have a number of cheap-ish supporting motherboards that often feature integrated video as standard. If your budget is set a little higher, say, at £80 for a processor (or ~£150 for a processor/motherboard bundle), AMD's K8-class Sempron 3100+ is comfortably the best choice. It's just a shame that it's been stripped of 64-bit goodness, though.
Check it out in full, here.
Rys